U.S. patent number 6,689,860 [Application Number 09/995,623] was granted by the patent office on 2004-02-10 for solid golf ball.
This patent grant is currently assigned to Sumitomo Rubber Industries Limited. Invention is credited to Satoshi Iwami.
United States Patent |
6,689,860 |
Iwami |
February 10, 2004 |
Solid golf ball
Abstract
There is provided a solid golf ball comprising a multi-piece
core and a cover made from polyurethane obtained by curing an
isocyanate group-terminated urethane prepolymer including a
residual polyisocyanate monomer content of not more than 0.1% by
mass using an aromatic polyamine curing agent. The golf ball
satisfies moldability of the polyurethane cover and durability, and
exhibits excellent ball characteristic such as flight performance
and shot feeling.
Inventors: |
Iwami; Satoshi (Kobe,
JP) |
Assignee: |
Sumitomo Rubber Industries
Limited (Kobe, JP)
|
Family
ID: |
18866777 |
Appl.
No.: |
09/995,623 |
Filed: |
November 29, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Dec 28, 2000 [JP] |
|
|
2000-402502 |
|
Current U.S.
Class: |
528/64; 473/373;
473/374; 473/378; 528/63 |
Current CPC
Class: |
A63B
37/0003 (20130101); C08G 18/10 (20130101); C08G
18/4854 (20130101); C08G 18/10 (20130101); C08G
18/3814 (20130101); A63B 37/0031 (20130101); A63B
37/0054 (20130101); A63B 37/0062 (20130101); A63B
37/0064 (20130101); A63B 37/0065 (20130101); A63B
37/0075 (20130101); A63B 37/02 (20130101); A63B
37/12 (20130101) |
Current International
Class: |
A63B
37/00 (20060101); C08G 18/00 (20060101); C08G
18/48 (20060101); C08G 18/10 (20060101); A63B
37/12 (20060101); A63B 37/02 (20060101); A63B
037/00 (); A63B 037/12 (); C08G 018/32 () |
Field of
Search: |
;528/63,64
;473/373,374,378 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Buttner; David J.
Claims
What is claimed is:
1. A solid golf ball comprising: a solid core comprising a solid
center made from vulcanized rubber and an intermediate layer
covering the solid center; and a cover covering the solid core,
wherein the solid center is a vulcanized rubber sphere having an
outer diameter of from 30.0 to 41.0 mm and a difference of not less
than 10 in Shore D hardness between a central portion thereof and a
surface portion thereof, and deforms from 2.80 to 6.00 mm by
compression on condition that an initial load of 10 kgf is
increased to an ultimate load of 130 kgf; the solid core has an
outer diameter of from 39.0 to 41.8 mm, deforms from 2.70 to 3.50
mm by compression on condition that an initial load of 10 kgf is
increased to an ultimate load of 130 kgf; the cover has an
outermost layer made from polyurethane obtained by curing a
composition comprising an isocyanate group-terminated urethane
prepolymer and an aromatic polyamine curing agent, the isocyanate
group-terminated urethane prepolymer having a residual
polyisocyanate monomer content of not more than 0.1% by mass and
the polyurethane has a Shore D hardness of from 35 to 60; and the
golf ball deforms from 2.50 to 3.30 mm by compression on condition
that an initial load of 10 kgf is increased to an ultimate load of
130 kgf.
2. The solid golf ball according to claim 1, wherein the aromatic
polyamine curing agent is 4,4'-diaminodiphethylmethane represented
by the formula: ##STR2##
where R.sup.1 to R.sup.8 each represent any one of an alkyl group
having 1 to 9 carbon atoms, a halogen atom, a hydrogen atom, and a
derivative thereof.
3. The solid golf ball according to claim 1, wherein the aromatic
polyamine curing agent is
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane.
4. The solid golf ball according to claim 1, wherein the isocyanate
group-terminated urethane prepolymer is one selected from the group
consisting of a TDI-type urethane prepolymer, an MDI-type urethane
prepolymer and a hydrogenated MDI-type urethane prepolymer.
5. The solid golf ball according to claim 1, wherein the
intermediate layer is an ionomer.
6. The solid golf ball according to claim 1, wherein the
intermediate layer is a thermoplastic elastomer.
7. The solid golf ball according to claim 1, wherein the solid
center has an outer diameter of from 32.0 to 40.8 mm.
8. The solid golf ball according to claim 1 wherein the solid
center has a Shore D hardness of 25 to 40 at the central portion
thereof.
9. The solid golf ball according to claim 1, wherein the solid
center has a Shore D hardness of 35 to 50 at the surface
thereof.
10. The solid golf ball according to claim 1, wherein the solid
center deforms from 2.90 to 5.5 mm by compression on condition that
an initial load of 10 kgf is increased to an ultimate load of 130
kgf.
11.The solid golf ball according to claim 1, wherein the solid core
has an outer diameter of from 39.6 to 41.0 mm.
12. The solid golf ball according to claim 1, wherein the solid
core deforms from 2.80 to 3.40 mm by compression on condition that
an initial load of 10 kgf is increased to an ultimate load of 130
kgf.
13. The solid golf ball according to claim 1, wherein the golf ball
deforms from 2.60 to 3.20 mm by compression on condition that an
initial load of 10 kgf is increased to an ultimate load of 130 kgf.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-piece solid golf ball
comprising a multi-layered core and a polyurethane cover covering
the core.
2. Description of the Related Art
A conventional solid golf ball has a solid core made from
vulcanized rubber and an ionomer resin cover because an ionomer
resin cover exhibits superior durability. Golf balls with ionomer
resin covers, however, give golfers a larger impact upon shot than
golf balls with Balata rubber covers and hence are likely to impart
the golfers with inferior shot feeling.
In attempt to improve the shot feeling imparted by golf balls with
the ionomer covers, Japanese Patent No. 2709950, for example, has
proposed a cover made from a mixture of a hard ionomer such as a
sodium salt or zinc salt of an olefin-unsaturated carboxylic acid
copolymer and a soft ionomer such as a sodium salt or zinc salt of
an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester terpolymer. The cover makes it possible to render the shot
feeling soft due to the soft ionomer in the cover material, but on
the other hand, impairs the merits inherent to ionomer covers; for
example, the repulsion property as well as the scuff resistance of
the golf ball lowers.
In recent years, polyurethane is receiving attention as an
inexpensive cover material that imparts to golfers a shot feeling
analogous to a shot feeling imparted by the Balata cover and has
higher durability than the Balata cover. U.S. Pat. No. 5,334,673,
for example, has disclosed a polyurethane cover formed by curing a
urethane prepolymer with a slow-reactive polyamine curing agent.
Also, Japanese Patent Laid-Open Gazette No. HEI 9-215778 has
proposed a cover made from thermoplastic polyurethane.
Polyurethane used as a cover material involves a problem that it
makes the molding of a cover difficult because the curing reaction
between a urethane prepolymer and a polyamine proceeds rapidly,
which causes a steep increase in viscosity. The U.S. Pat. No.
5,334,673 has solved the problem by the use of a slow-reactive
polyamine and/or a glycol. In the art of the publication, however,
there are some cases depending on kinds of urethane prepolymer,
curing agent, and/or combinations thereof in which an increase in
viscosity is still rapid and makes the molding of a cover
difficult. Even though a polyurethane cover is obtained by molding,
a golf ball with the resulting cover is not sufficient in terms of
repulsion property, spin performance and scuff resistance. Thus,
further improvements with respect to a thermosetting type
polyurethane cover are desired.
Thermoplastic polyurethane elastomers used as cover materials are
superior in moldability to thermosetting polyurethane covers, but
are inferior in wear resistance, tear strength and scuff resistance
to thermosetting polyurethane covers or hard ionomer covers because
of the lack of three-dimensionally crosslinking points.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solid golf ball
with a cover made from polyurethane which is satisfactory in
moldability and ball characteristics.
A solid golf ball of the present invention comprises a solid core
comprising a solid center made from vulcanized rubber and an
intermediate layer covering the solid center, and an cover covering
the solid core. The cover has an outermost layer made from
polyurethane obtained by curing a composition comprising an
isocyanate group-terminated urethane prepolymer and an aromatic
polyamine curing agent. The isocyanate group-terminated urethane
prepolymer has a residual polyisocyanate monomer content of not
more than 0.1% by mass.
The foregoing and other objects, features and attendant advantages
of the present invention will become apparent from the reading of
the following detailed description.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic view showing the appearance of a golf ball
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail.
According to the solid golf ball of the present invention, as shown
in FIG. 1, a solid core 3 is covered with a specific polyurethane
cover 4. The core 3 comprises a solid center 1 and an intermediate
layer 2 placed on the center 1.
The polyurethane cover is formed by curing a composition comprising
an aromatic polyamine curing agent and an isocyanate
group-terminated urethane prepolymer. The isocyanate
group-terminated urethane prepolymer contains a residual
polyisocyanate monomer in an amount of not more than 0.1% by
mass.
The "isocyanate group-terminated urethane prepolymer " of the
invention means a urethane prepolymer has at least two isocyanate
groups in its molecular chain. Each isocyanate group may be located
at the terminal of the backbone chain of the molecular chain or at
the terminal of a side chain of the urethane prepolymer. The
isocyanate group-terminated urethane prepolymer is prepared by a
reaction between a polyol and a polyisocyanate compound in a state
where the isocyanate group of the polyisocyanate compound is
excessive relative to the hydroxyl group of the polyol in molar
ratio.
The "residual polyisocyanate monomer", as used herein, means an
unreacted polyisocyanate compound remaining in the isocyanate
group-terminated urethane prepolymer. The content of the residual
polyisocyanate monomer in the isocyanate group-terminated urethane
prepolymer is defined by the expression: (the mass of the residual
polyisocyanate monomer/the mass of the isocyanate group-terminated
urethane prepolymer including the residual polyisocyanate monomer
and the like).times.100 and can be determined by gas
chromatography. If the content of the residual polyisocyanate
monomer is more than 0.1% by mass, a precipitate is likely to occur
in the urethane cover composition before finishing the curing
reaction. Though the mechanism of occurrences of the precipitate is
not clearly known, it can be presumed that the residual
polyisocyanate monomer reacts with the polyamine curing agent to
precipitate the reaction product. Such precipitation causes uneven
reaction between the isocyanate group-terminated urethane
prepolymer and the polyamine curing agent, resulting in a
difficulty in the manufacture of a homogeneous polyurethane cover.
A heterogeneous polyurethane cover has affected durability,
particularly a lowered scuff resistance. In an extreme case, the
composition for a cover is cured before forming a cover, which
makes the molding of the cover substantially impossible.
Examples of the polyisocyanate compounds for use as raw materials
of isocyanate group-terminated urethane prepolymers include,
without any particular limitation, aromatic diisocyanates such as
TDI (toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, or a
mixture thereof), MDI (4,4'-diphenylmethane diisocyanate or a
polynuclear compound thereof), 1,5-naphthylene diisocyanate (NDI),
3,3'-bitolylene-4,4'-diisocyanate (TODI), xylylene diisocyanate
(XDI) and paraphenylene diisocyanate (PPDI); and alicyclic
diisocyanates or aliphatic diisocyanates such as
4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI),
hexamethylene diisocyanate (HDI) and isophorone diisocyanate
(IPDI), or mixtures of one or two or more of them. Among them, TDI
or hydrogenated MDI is preferably used because a resulting
polyurethane cover has favorable mechanical properties and a golf
ball with the resulting polyurethane cover is satisfactory in
repulsion property, weatherability and water resistance.
Any polyol having a plurality of hydroxyl groups may be used as a
raw material of the isocyanate group-terminated urethane prepolymer
regardless of whether it is a low-molecular-weight compound or a
high-molecular-weight compound. Examples of the
low-molecular-weight polyols include diols such as ethylene glycol,
diethylene glycol, triethylene glycol, 1,3-butanediol,
1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and triols
such as glycerin, trimethylolpropane, and hexanetriol. Examples of
the high-molecular-weight polyols include polyether polyols
generally resulting from the reaction between an initiator having
active hydrogen and alkylene oxide; condensed polyester polyols
generally resulting from the dehydro-condensation between a dibasic
acid such as adipic acid, and a glycol or a triol; lactone
polyester polyols generally resulting from ring opening
polymerization of a lactam such as .epsilon.-caprolactam;
polycarbonate diols generally synthesized using a cyclic diol; and
polymer polyols such as an acrylic polyol prepared by introducing
an appropriate hydroxyl group into an acrylic copolymer. Examples
of specific polyether polyols include polyoxyethylene glycol,
polyoxypropylene glycol (PPG), and polyoxytetramethylene ether
glycol (PTMG). Examples of specific condensed polyester polyols
include polyethylene adipate (PEA), polybutylene adipate (PBA), and
polyhexamethylene adipate (PHMA). Examples of specific lactone
polyester polyols include poly-.epsilon.-caprolactone (PCL). In
view of their superior repulsion property and water resistance,
polyether polyols are preferable. Use of polyoxytetramethylene
ether glycol is particularly preferable.
Accordingly, one selected from the group consisting of a TDI-type
urethane prepolymer, an MDI-type urethane prepolymer and a
hydrogenated MDI-type urethane prepolymer is preferably used as the
isocyanate group-terminated urethane prepolymer. Specifically, use
of a TDI-type urethane prepolymer, an MDI-type urethane prepolymer,
a hydrogenated MDI-type urethane prepolymer, a mixture of a
TDI-type urethane prepolymer and hydrogenated MDI-type urethane
prepolymer, or the like is preferable.
The "TDI-type urethane prepolymer", as used herein, means an
isocyanate group-terminated urethane prepolymer resulting from the
reaction between a TDI or a polyisocyanate compound comprising a
TDI as a major component and a polyol (preferably
polytetramethylene ether glycol). The "MDI-type urethane
prepolymer", as used herein, means an isocyanate group-terminated
urethane prepolymer resulting from the reaction between an MDI or a
polyisocyanate compound comprising an MDI as a major component and
a polyol (preferably polytetramethylene ether glycol). The
"hydrogenated MDI-type urethane prepolymer", as used herein, means
an isocyanate group-terminated urethane prepolymer resulting from
the reaction between a hydrogenated MDI or a polyisocyanate
compound comprising a hydrogenated MDI as a major component and a
polyol (preferably polytetramethylene ether glycol).
Specific examples of the isocyanate group-terminated urethane
prepolymer having a residual polyisocyanate monomer content of not
more than 0.1% by mass includes Adiprene LF900A and LF950A
available from UNIROYAL CHEMICAL.
The aromatic polyamine curing agent used in the present invention
is a compound having at least two amino groups bonded to aromatic
ring(s). Such a compound may be of a phenylenediamine type in which
two or more amino groups are bonded to one aromatic ring or of a
polyaminobenzene type that contains two or more aminophenyl groups
in each of which one amino group is bonded to one aromatic ring.
Polyaminobenzene-type compounds are preferable because they have
less influence of amino groups upon each other or less influence of
steric hindrance. Such a polyaminobenzene-type compound may be
diaminobenzene in which two aminophenyl groups are directly bonded
to each other or may be such that two aminophenyl groups are bonded
to each other through a lower alkylene group or an alkylene oxide
group. Among them, diaminodiphenylalkane having two aminophenyl
groups bonded to each other through a lower alkylene group.
Particularly preferable are 4,4'-diaminodiphenylmethane represented
by the following general formula or derivatives thereof. In the
case where the compound is of p-form and having a not very long
molecular chain intervening between aminophenyl groups, benzene
nuclei forming hard segments can be arranged side-by-side linearly
on a plane and, hence, it is possible to efficiently make use of
urethane bond, urea bond, hydrogen bond between benzene nuclei or
intermolecular cohesive energy, thus resulting in improvements in
repulsion property, tensile strength and tear strength. For this
reason, a resulting cover tends to be improved in cover strength
such as scuff resistance, and cover durability. ##STR1##
R.sup.1 to R.sup.8 each represent any one of an alkyl group having
1 to 9 carbon atoms, a halogen atom or a hydrogen atom.
Specific examples of such alkyl group having 1 to 9 carbon atoms
include straight-chain alkyl groups such as methyl, ethyl,
n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and
n-nonyl; branched-chain alkyl groups such as i-propyl, i-butyl,
sec-butyl, t-butyl, and neopentyl; and alicyclic alkyl groups such
as cyclopropyl and cyclohexyl. Among them, methyl and ethyl are
preferable as they involve less steric hindrance. Examples of such
halogen atoms include fluorine, chlorine, bromine, and iodine.
Among them, chlorine and bromine are preferable. R.sup.1 to R.sup.8
may be different alkyl groups or different halogen atoms. Examples
of derivatives of 4,4'-diaminodiphenylmethane include
3,3'-dichloro-4,4'-diaminodiphenylmethane,
3,3'-dimethyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3',
5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 3,3',
5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3',
5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane,
3,3'-dimethyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane,
3,3'-diethyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane,
3,3'-dimethyl-5,5'-di-t-butyl-4,4'-diaminodiphenylmethane,
3,3'-dichloro-5,5'-diethyl-4,4'-diaminodiphenylmethane,
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, and
2,2',3,3'-tetrachloro-4,4'-diaminodiphenylmethane. Among them,
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane is
particularly preferable because its toxicity is low.
Though the amount of the aromatic polyamine curing agent in the
composition used for the cover is not particularly limited,
preferably the aromatic polyamine curing agent is blended with the
isocyanate group-terminated urethane prepolymer so that the molar
ratio of amino group of the polyamine respective to isocyanate
group of the urethane prepolymer, namely NH.sub.2 /NCO, is 0.85 to
1.15.
The composition used for the cover in the present invention may
contain any conventionally known catalyst for use in a curing
reaction between polyisocyanate and polyamine. Examples of such
catalysts include monoamines such as triethylamine and
N,N-dimethylcyclohexylamine; polyamines such as
N,N,N',N'-tetramethylethylenediamine and
N,N,N',N",N"-pentamethyldiethylenetriamine; cyclic diamines such as
1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) and triethylenediamine;
organic carboxylic acids such as azelaic acid, oleic acid, and
adipic acid; and tin catalysts such as dibutyltin dilaurylate and
dibutyltin diacetate. Among them, azelaic acid is preferably
used.
As required, the composition for cover may contain, in addition to
the isocyanate group-terminated urethane prepolymer and the
aromatic polyamine curing agent, a filler such as barium sulfate, a
coloring agent such as titanium dioxide, and other additives such
as a dispersant, antioxidant, ultraviolet absorber, light
stabilizer, fluorescent material, and fluorescent brightener unless
they impair any desired property to be imparted to an intended golf
ball by a resulting cover.
With respect to the cover of the golf ball according to the present
invention, the hardness of the cover material polyurethane alone
(the hardness of the material itself may be referred to as "slab
hardness") is preferably not less than 35, more preferably not less
than 40, much more preferably not less than 43, in terms of Shore D
hardness. If the hardness is less than 35, the resulting cover is
so soft that a golf ball with this cover is easy to spin and hence
exhibits a lowered repulsion property and that the cover exhibits
too low a scuff resistance (scuff resistance) when hit with an iron
or a sand wedge. Since a polyurethane having a higher slab hardness
gives a harder cover, too high a slab hardness results in a golf
ball which offers a harder shot feeling and which cannot ensure
satisfactory controllability in approach shots due to the spin rate
decreased too much. For this reason, the upper limit of the slab
hardness (Shore D hardness) of the cover material polyurethane is
preferably 60, more preferably 55, much more preferably 52.
The isocyanate group-terminated urethane prepolymer and the
aromatic polyamine curing agent need to react in a state that they
are homogeneously mixed. It is therefore preferable to mix the
melted polyamine compound with the urethane prepolymer which is
heated to a temperature close to the temperature of the melted
polyamine, and inject the mixture into a mold heated to a
temperature close to the mixing temperature.
The solid core used in the present invention is a multi-piece solid
core formed by covering a solid center of a vulcanized rubber
sphere with at least one intermediate layer.
Employing such a multi-piece solid core can provide a difference in
hardness between a central portion and a surface portion of the
core more easily than the case of adjustment of the difference in
hardness between a central portion and a surface portion of a
single-layered core. Further, by adjusting the respective
compositions and thicknesses of the solid center and the
intermediate layer, it is possible to widen the freedom of hardness
distribution and hence to provide a considerably large difference
in hardness between the solid core center (i.e. central point of
the solid center) and the solid core surface (i.e. surface of the
outermost intermediate layer). By varying the respective materials
of the solid center and the intermediate layer, it is possible to
optimize a spin rate of a resulting golf ball. For the reasons
stated above, it is possible to combine a polyurethane cover with a
solid core having a hardness distribution that is suited to the
sort of the polyurethane cover. Comparing a multi-piece solid core
with a single-layered core having a substantially equal hardness
(deformable amount) to one of the multi-piece core as its entirety,
a multi-piece solid core may provide a golf ball exhibiting more
excellent flying performance suited for various clubs. For example,
a golf ball with such a multi-piece solid core can realize a higher
shot angle and a smaller spin rate when hit with a driver or an
iron while ensuring an adequate spin rate when hit with a sand
wedge.
A multi-piece solid core suitably combined with the aforementioned
polyurethane cover has the following structure.
Next, the solid core used in the inventive golf ball will be
described.
The solid center is made of vulcanized rubber sphere and forms a
core portion of the multi-piece solid core. The preferable solid
center has an outer diameter of not less than 30.0 mm, more
preferably not less than 31.0 mm, much more preferably not less
than 32.0 mm. The upper limit of the outer diameter of the solid
center is preferably 41.0 mm, more preferably 40.8 mm, much more
preferably 40.8 mm. If the center has an outer diameter of less
than 30.0 mm is too small, it is difficult to provide a desired
difference in hardness between the central point and the surface of
the solid center. On the other hand, if the outer diameter of the
solid center is more than 41.0 mm, the intermediate layer and the
cover are required to be thin because the size of a golf ball is
prescribed, resulting in a difficulty in molding.
The solid center is preferably made to become softer as it extends
toward the central point thereof. The difference in Shore D
hardness between the central point and the surface of the solid
center is preferably not less than 10 and not more than 25, more
preferably not less than 12 and not more than 20. The amount of
deformation of the solid center applied with a load varying from 10
kgf as an initial load to 130 kgf as a final load, which serves an
indication of the softness of the whole solid center, is preferably
not less than 2.80 mm and not more than 6.00 mm, more preferably
not less than 2.90 mm and not more than 5.5 mm, much more
preferably not more than 5.0 mm.
By adjusting the difference in hardness between the central point
and the surface of the solid center and the amount of deformation
of the solid center so as to fall within the respective ranges
stated above, it is possible to enhance the repulsion property of
the resulting golf ball as well as to ensure a soft shot feeling
when the ball is hit with a wood or an iron.
Any solid center satisfying the foregoing requirements may be used
in the present invention. Specifically, the hardness of the central
portion of the solid center is preferably from 25 to 40, more
preferably from 28 to 38, while the hardness of the surface of the
solid center is preferably from 35 to 50, more preferably from 38
to 48.
The rubber composition for the solid center may be any rubber
composition generally used for the core of a conventional solid
golf ball. Specifically, such a rubber composition comprises a
diene rubber such as butadiene rubber (BR),
ethylene-propylene-diene terpolymer (EPDM), isoprene rubber (IR),
styrene-butadiene rubber (SBR), or acrylonitrile-butadiene rubber
(NBR); an unsaturated carboxylic acid and/or a metal salt thereof
as a co-crosslinking agent; an organic peroxide as a crosslinking
initiator; and optionally other additives such as a specific
gravity adjustor.
Examples of the organic peroxides include dicumyl peroxide,
1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexanei,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.
Among them, dicumyl peroxide is preferably used. The amount of the
organic peroxide to be blended is preferably from 0.1 to 3.0 parts
by mass, more preferably from 0.2 to 2.0 parts by mass, based on
100 parts by mass of the diene rubber.
Preferable as the unsaturated carboxylic acid is an .alpha.,
.beta.-unsaturated carboxylic acid having 3 to 8 carbon atoms such
as an acrylic acid or a methacrylic acid. A preferable metal salt
of the unsaturated carboxylic acid is a monovalent or bivalent
metal salt such as a zinc salt or magnesium salt. The amount of the
unsaturated carboxylic acid and/or a metal salt thereof is
preferably from 15 to 40 parts by mass, particularly from 20 to 35
parts by mass, based on 100 parts by mass of the diene rubber.
The vulcanization conditions for the rubber composition are
appropriately established depending on the formulation of the
rubber composition. Preferably vulcanization is performed at
160.degree. C. to 180.degree. C. for 10 to 25 minutes to obtain a
solid center satisfying the foregoing hardness conditions.
The intermediate layer in a state that covers the solid center to
form a multi-piece solid core satisfies the following conditions.
Specifically, the diameter of such a multi-piece solid core is
preferably not less than 39.0 mm and not more than 41.8 mm, more
preferably not less than 39.6 mm and not more than 41.6 mm, much
more preferably not less than 40.0 mm and not more than 41.0 mm.
The amount of deformation of the multi-piece solid core applied
with a load varying from 10 kgf as an initial load to 130 kgf as a
final load is preferably not less than 2.70 mm, more preferably
2.80 mm, much more preferably 2.90 mm. The upper limit of the
amount of deformation is preferably 3.50 mm, more preferably 3.40
mm, much more preferably 3.30 mm. Such a core having a larger
diameter and larger variation in hardness may provide a golf ball
that exhibits a reduced spin rate, hence an enhanced repulsion
property thereby ensuring a satisfactory flight distance without
impairing the softness when hit with a wood or an iron while
ensuring a required spin rate when hit with a sand wedge. If the
core diameter is less than 39.0 mm, the intermediate layer is
required to be thin due to the relation to the solid center, which
makes it difficult to provide an effect. Besides, the cover is
required to be thick. As a result, a golf ball easily spins and
exhibits too low a repulsion property. On the other hand, if it is
more than 41.6 mm, the cover is required to be thin, which results
in a difficulty in molding.
The amount of deformation of the core is an indication of the
softness of the whole core. Even if the hardness of the core
surface is increased, the resulting golf ball can impart a soft
shot feeling to the golfer without impairing a repulsion property
so long as the amount of deformation is adjusted to fall within the
aforementioned range.
The intermediate layer used in the present invention may be any
intermediate layer that can provide a multi-piece solid core
satisfying the aforementioned requirements. The intermediate layer
may be made from a vulcanized rubber, a resin such as an ionomer or
a thermoplastic elastomer, or a mixture of a rubber and a resin. In
order that the solid center and the core satisfy the foregoing
respective requirements, the thickness of the intermediate layer is
preferably from 0.4 to 9.0 mm, more preferably from 0.5 to 5.0 mm,
much more preferably 0.5 to 4.0 mm. If the thickness of the coating
layer is less than 0.4 mm, a difficulty arises in molding. If it is
more than 9.0 mm, a resulting solid core is likely to have a lower
repulsion property than a single-layered solid core made from
vulcanized rubber unless the intermediate layer is formed of a
vulcanized rubber.
According to the present invention, the amount of deformation of
the golf ball is preferably not less than 2.50 mm, more preferably
2.60 mm, much more preferably 2.70 mm when applied with a load
varying from 10 kgf as an initial load to 130 kgf as a final load.
The upper limit of the amount of deformation is preferably 3.30 mm,
more preferably 3.20 mm, much more preferably 3.10 mm. A golf ball
of which the amount of deformation is less than 2.50 mm is so hard
that the golfer hitting this ball receives too large an impact. On
the other hand, a golf ball of which the amount of deformation is
more than 3.30 mm is so soft that the length of time from the
moment the ball is hit to the moment the ball departs from the face
of the club is prolonged and hence the golfer feels the ball
heavy.
The solid golf ball of the present invention may be manufactured by
a process conventionally known as a process for manufacturing a
golf ball covered with a hard polyurethane cover. Specifically, a
cover composition is injected into a hemispherical mold holding
therein the core and then the mold is inverted and jointed with
another hemispherical mold into which a polyurethane cover
composition has been injected, to form a golf ball with a
polyurethane cover.
As required, the surface of the polyurethane cover is formed with a
multiplicity of dimples during the molding of the cover. Further,
the golf ball of the present invention is usually provided with
paint finish, a marking stamp and the like to enhance the
appearance and commercial value thereof before it is put on the
market.
It is to be noted that the cover of the golf ball of the present
invention may comprise a single layer or plural layers.
According to the present invention, the solid golf ball has a
polyurethane cover formed using a urethane prepolymer having a
residual polyisocyanate monomer content of not more than 0.1% by
mass and hence is excellent in scuff resistance and durability.
Further, since the solid golf ball has a multi-layered core which
allows the hardness distribution thereof and the amount of
deformation thereof to be adjusted to fall within respective
appropriate ranges, the ball can exhibit superior flying
performance when hit with any one of various clubs such as a wood,
iron and sand wedge.
EXAMPLES
Hereinafter, the present invention will be more specifically
described by way of examples, which are, in no way, construed as
limitative of the present invention.
Measurement and Evaluation Methods
1. Amount of Compressive Deformation (mm)
The amount of deformation of a solid center, a core or a golf ball
by compressing on condition that an initial load of 10 kgf is
increased to an ultimate load of 130 kgf was measured.
2. Shore D Hardnesses of the Central Point and the Surface of a
Solid Center, and the Surface of a Core
Measurement was performed using a Shore D type spring hardness
tester prescribed by ASTM-D2240.
The solid center was divided into two hemispherical halves and the
hardness of one of the hemispherical halves was measured by
pressing a pick against the central point of the halves. The
hardness of the surface of the solid center was measured by
pressing the pick against the surface of the solid center. The
hardness of the surface of the core was measured by pressing the
pick against the surface of the core in a state where the solid
center was covered with the intermediate layer.
3. Hardness of a Cured Product of a Cover Composition (Slab
Hardness)
The composition prepared for cover was formed into sheets each
having a thickness of about 2 mm by hot press molding and the
resulting sheets were conserved at 23.degree. C. for two weeks.
Three or more of the sheets were stacked on one another to prevent
the substrate or the like used in the measurement from influencing
the measurement and the stack was subjected to measurement using
the Shore D type spring hardness tester prescribed by
ASTM-D2240.
4. Flying Performance of a Golf Ball
A golf ball was hit with a wood (W#1) attached to a swing robot
manufactured by True Temper Co., Ltd. at a head speed of 50 m/sec.
The shot angle (.degree.), spin rate (rpm) and flight distance (the
distance (m) from the hitting point to the point at which the ball
stopped after its falling to the ground) of the golf ball thus hit
were measured.
In turn, the golf ball was hit with an iron (I#5) attached to the
swing robot instead of the wood at a head speed of 41 m/sec. The
shot angle (.degree.), spin rate (rpm) and flight distance (the
distance (m) from the hitting point to the point at which the ball
stopped after its falling to the ground) of the golf ball thus hit
were measured.
Thereafter, the golf ball was hit with a sand wedge (SW) attached
to the swing robot instead of the iron at a head speed of 21 m/sec.
The spin rate (rpm) of the golf ball thus hit was measured.
5. Scuff Resistance
Two portions of a golf ball were each hit once using a commercially
available pitching wedge attached to the swing robot at a head
speed of 36 m/sec. The condition of each of the two portions thus
hit was visually observed and rated into three categories according
to the following criteria. The lower one of the two ratings was
regarded as the rating of the golf ball. Category ".largecircle.":
a ball surface with few flaws left to an unnoticeable degree.
Category ".DELTA.": a ball surface with clearly noticeable flaws
and with slight napping observed. Category "X": a ball surface
considerably shaved and conspicuously napped.
Manufacture of Golf Ball
Each of solid center rubber compositions (C1 to C4) of the
formulation shown in Table 1 was subjected to vulcanizing molding
at 170.degree. C. for 15 minutes, to form a solid center.
The solid center thus formed was covered with an intermediate layer
composition (H1 or H2) shown in Table 2, to form a double-layered
core.
The core thus formed was covered with each of cover compositions
(P1 to P6) shown in Table 3 by a molding process, to form a golf
ball having a diameter of 42.8 mm.
TABLE 1 Solid center composition C1 C2 C3 C4 BR-18 100 100 100 100
Zinc acrylate 32 30 30 28 Zinc white 12.0 13.0 21.0 17.0 Diphenyl
disulfide 0.5 0.5 0.5 0.5 Dicumyl peroxide 1.0 1.0 1.0 1.0
In Table 1, BR-18 is a high-cis-polybutadiene produced by JSR Co.,
Ltd. used as a butadiene rubber; diphenyl disulfide is a product of
Sumitomo Seika Co., Ltd. and dicumyl peroxide is a product of NOF
CORPORATION.
TABLE 2 Intermediate Layer H1 H2 BR-11 80 -- BR-10 20 -- Zinc
acrylate 38 -- Zinc oxide 10.5 -- Dicumyl peroxide 0.5 -- Himilan
1605 -- 60 Himilan 1706 -- 40
In Table 2, BR-11 and BR-10 are polybutadiene rubbers produced by
JSR Co., Ltd.; Himilan 1605 is a sodium ion-neutralized
ethylene-methacrylic acid type ionomer resin produced by
Mitui-DuPont Polychemical Co., Ltd; and Himilan 1706 is a zinc
ion-neutralized ethylene-methacrylic acid type ionomer resin
produced by Mitui-DuPont Polychemical Co., Ltd.
TABLE 3 Cover composition P1 P2 P3 P4 P5 P6 Urethane prepolymer
Adiprene LF900A 80 80 -- -- -- -- Adiprene LF950A 20 20 -- -- -- --
Adiprene L100 -- -- 100 -- -- -- Vibrathane B635 -- -- -- 100 -- --
Curing agent Lonzacure M-CDEA 17.8 -- 17.9 -- -- -- Elasmer-250P --
21.7 -- -- -- -- 1,4-butanediol -- -- -- 7.9 -- -- Elastomer Pandex
T1198 -- -- -- -- 100 -- Surlyn 8120 -- -- -- -- -- 50 Himilan
AM7316 -- -- -- -- -- 50 Titanium oxide 2 2 2 2 2 2 Curing time
(min) 10 15 10 20 -- -- Mold temperature (.degree. C.) 100 100 100
10 -- -- Prepolymer temperature 80 80 80 80 -- -- (.degree. C.)
Curing agent temperature 120 120 50 60 -- -- (.degree. C.) Slab
hardness (Shore D) 43 44 42 43 42 43
In Table 3, Adiprene LF900A is a TDI(NCO content=3.7%)-PTMG type
prepolymer having a free TDI content of not more than 0.1% produced
by UNIROYAL CHEMICAL; Adiprene LF950A is a TDI(NCO
content=6.1%)-PTMG type prepolymer having a free TDI content of not
more than 0.1% produced by UNIROYAL CHEMICAL; Vibrathane B635 is a
MDI(NCO content=7.5%)-PTMG type prepolymer having a free MDI
content of more than 0.1% produced by UNIROYAL CHEMICAL; Adiprene
L100 is a TDI(NCO content=4.1%)-PTMG type prepolymer having a free
TDI content of more than 0.1% produced by UNIROYAL CHEMICAL;
Lonzacure M-CDEA is 4,4'-methylenebis(3-chloro-2,6-diethylaniline)
having an amine number of 297 mgKOH/g produced by UNIROYAL
CHEMICAL; Elasmer 250P is polytetramethylene oxide aminobenzoate
having an amine value of 249.4 mgKOH/g produced by AIR PRODUCTS
CO.; Pandex T1198 is an adipate-type thermoplastic polyurethane
elastomer produced by Dainippon Ink & Chemicals; Surlyn 8120 is
an Na ion-neutralized methacrylic acid type three-component ionomer
produced by Dupont Co., Ltd.; and Himilan AM7316 is an Mg
ion-neutralized methacrylic acid type three-component ionomer
produced by Mitui-DuPont Polychemichal Co., Ltd.
The structures and characteristics of golf balls manufactured as
Examples Nos. 1 to 9 of the present invention are collectively
shown in Table 4, while the structures and characteristics of golf
balls manufactured as Comparative Examples Nos. 1 to 5 are shown in
Table 5.
It should be noted that Comparative Example No. 5 was a golf ball
having a single-layered core formed from solid center composition
C1.
TABLE 4 Example ball No 1 2 3 4 5 6 7 8 9 Solid center Type of
composition C1 C2 C1 C2 C2 C3 C4 C1 C2 Diameter (mm) 33.8 37.8 33.2
37.2 37.2 37.2 39.6 32.8 36.8 Amount of deformation (mm) 4.55 3.70
4.50 3.65 3.65 3.65 3.45 4.45 3.60 Hardness at center 34 35 34 35
35 35 35 34 35 Hardness at the surface 45 47 45 47 47 47 50 50 47
Difference in hardness 11 12 11 12 12 12 15 16 12 Intermediate
layer Type of composition H1 H1 H1 H1 H1 H2 H2 H1 H1 Thickness (mm)
4.0 2.0 4.0 2.0 2.0 2.0 0.8 4.0 2.0 Diameter (mm) 41.8 41.8 41.2
41.2 41.2 41.2 41.2 40.8 40.8 Hardness at surface 55 55 55 55 55 70
70 55 55 Amount of deformation (mm) 3.19 3.20 3.14 3.15 3.15 3.05
2.75 3.09 3.15 Cover Type P1 P1 P1 P1 P2 P2 P2 P2 P2 Thickness (mm)
0.5 0.5 0.8 0.8 0.8 0.8 0.8 1.0 1.0 Slab hardness 43 43 43 43 44 44
44 44 44 Ball Amount of deformation (mm) 2.99 3.00 2.90 2.92 2.93
2.83 2.53 2.84 2.85 Initial velocity 72.1 72.3 71.9 72.2 71.9 72.6
72.9 71.5 71.7 Shot angle (W#1) 9.9 10.0 9.8 9.8 9.7 9.7 9.8 9.7
9.7 Spin rate (W#1) 2200 2100 2300 2200 2300 2450 2400 2350 2300
Flight distance (W#1) 234 235 232 233 231 232 234 230 231 Shot
angle (I#5) 12.6 12.7 12.5 12.5 12.4 12.5 12.6 12.4 12.4 Spin Rate
(I#5) 4800 4700 4900 4800 4900 5000 4900 5000 4900 Flight distance
(I#5) 194 195 192 193 192 192 194 190 191 Spin rate (SW) 7000 6980
7050 7000 7050 7100 7000 7100 7050 Scuff resistance .largecircle.
.largecircle. .largecircle. .largecircle. .DELTA. .largecircle.
.largecircle. .largecircle. .largecircle.
TABLE 5 Comparative Ball No. 1 2 3 4 5 Solid center Type of
composition C2 C2 C2 C2 C2 Diameter (mm) 36.8 36.8 36.8 36.8 41.2
Amount of deformation (mm) 3.60 3.60 3.60 3.60 3.15 Hardness at
center 35 35 35 35 34 Hardness at the surface 47 47 47 47 49
Difference in hardness 12 12 12 12 12 Intermediate Layer Type of
composition H1 H1 H1 H1 -- Thickness (mm) 2.0 2.0 2.0 2.0 -- Core
Diameter (mm) 40.8 40.8 40.8 40.8 41.2 Hardness at surface 55 55 55
55 49 Amount of deformation (mm) 3.15 3.15 3.15 3.15 3.15 Cover
Type P3 P4 P5 P6 P1 Thickness (mm) 1.0 1.0 1.0 1.0 1.0 Slab
hardness 42 43 42 43 43 Ball Amount of deformation (mm) 2.92 2.91
2.91 2.89 2.93 Initial velocity 71.4 71.0 70.8 70.4 71.3 Shot angle
(W#1) 9.6 9.5 9.5 9.4 9.2 Spin rate (W#1) 2400 2450 2500 2550 2600
Flight distance (W#1) 229 227 225 224 222 Shot angle (I#5) 12.3
12.2 12.1 12.1 11.9 Spin rate (I#5) 5050 5200 5300 5400 5500 Flight
distance (I#5) 189 187 185 184 183 Spin rate (SW) 7050 7100 7400
7450 7500 Scuff resistance .DELTA. .DELTA. .DELTA. X
.largecircle.
Any one of Example golf balls Nos. 1 to 9 each comprising a
double-layered core consisting of a solid center and an
intermediate layer and a cover formed from cover composition P1 or
P2 using a urethane prepolymer having a residual polyisocyanate
mononer (free TDI) content of not more than 0.1% was superior in
scuff resistance to Comparative Example golf balls Nos. 3 and 4
each having a cover formed from a thermoplastic urethane elastomer
or a soft ionomer. In spite of the fact that Example golf ball No.
9 was in common with Comparative Example golf balls Nos. 3 and 4 as
to core composition, core diameter, core surface hardness and
deformation amount, Example golf ball No. 9 exhibited a higher shot
angle and a longer flight distance when hit with a wood or an iron
than Comparative Example golf balls Nos. 3 and 4. Further, Example
golf ball No. 9 exhibited an adequate spin rate (about 7000 rpm)
when hit with a sand wedge. This tendency holds true for other
Example golf balls. That is, any one of Example golf balls Nos. 1
to 9 was capable of ensuring a high shot angle and a long flight
distance when hit with a wood and an iron both while exhibiting an
adequate spin rate as large as about 7000 rpm when hit with a sand
wedge.
Any one of Comparative Example golf balls Nos. 1 and 2 each having
a cover of a polyurethane, which however was prepared using a
urethane prepolymer having a residual polyisocyanate monomer (free
TDI or free MDI) content of more than 0.1%, exhibited an inferior
scuff resistance. Further, these Comparative Example golf balls
each exhibited a slightly larger spin rate, a somewhat lower shot
angle and a somewhat shorter flight distance than Example golf ball
No. 9 having an identical core with those of Comparative Example
golf balls Nos. 1 and 2.
Comparative Example golf ball No. 5 having a polyurethane cover
formed using a urethane prepolymer having a residual polyisocyanate
monomer (free TDI) content of less than 0.1% exhibited an excellent
scuff resistance as did Example golf balls. However, since
Comparative Example golf ball No. 5 had a single-layered core, it
exhibited a larger spin rate when hit with any one of wood, iron
and sand wedge and a shorter flight distance when hit with wood or
iron than Example golf balls Nos. 3 to 5 each having a core which
was equal in diameter and substantially equal in hardness to
Comparative Example golf ball No. 5 but was of a double-layered
structure.
This application is based on Japanese Application Serial No.
2000-402502 filed in Japanese Patent Office on Dec. 28, 2000, the
contents of which are hereby incorporated by reference.
While only certain preferred embodiments of the present invention
have been described in detail, as will be apparent for those
skilled in the art, certain changes and modifications may be made
in embodiment without departing from the spirit and scope of the
present invention as defined by the following claims.
* * * * *